1. Field of the Invention
This present invention generally relates to laser scanning systems for reading data in the form of indicia such as bar code symbols and, more particularly, to a compact, integrated light source and scanning element implemented on a single semiconductor and/or electro-optical substrate.
2. Description of the Related Art
Various optical readers and optical scanning systems have been developed heretofore for reading bar code symbols appearing on a label or on the surface of an article. The bar code symbol itself is a coded pattern of indicia comprised of a series of bars of various widths spaced apart from one another to bound spaces of various widths, the bars and spaces having different light-reflecting characteristics. A number of different bar code standards or symbologies exist. These symbologies include UPC/EAN, Code 128, Codabar, and Interleaved 2 of 5. The readers and scanning systems electro-optically decode the symbol to multiple alphanumerical characters that are intended to be descriptive of the article or some characteristic thereof. Such characters are typically represented in digital form as an input to a data processing system for applications in point-of-sale processing, inventory control, and the like. Scanning systems of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,409,470 and U.S. Pat. No. 4,460,120, all of which have been assigned to the same assignee as the instant application.
As disclosed in some of the above patents, one embodiment of such a scanning system resides, in a device that emits a laser light beam from a hand-held, portable laser scanning head supported by a user, and aiming the head, and more particularly, the laser light beam, at a symbol to be read. The scanner functions by repetitively scanning the laser beam in a line across the symbol. A portion of the reflected laser light which is reflected off the symbol is detected, and electronic circuitry or software decodes the electrical signal into a digital representation of the data represented by the symbol scanned.
More specifically, a scanner includes a light source such as a gas laser or semiconductor laser that generates a light beam. The use of a semiconductor devices as the light source in scanner systems is especially desirable because of their small size, low cost and low power requirements. The light beam is optically modified, typically by a lens, to form a beam spot of a certain size. It is preferred that the beam spot size be approximately the same as the minimum width between regions of different light reflectivity, i.e., the bars and spaces of the symbol. The relative size of the bars and spaces is determined by the type of coding used, as is the actual size of the bars and spaces. The number of characters per inch represented by the bar code symbol is referred to as the density of the symbol.
The light beam is directed by the lens or similar optical components along a light path toward a target that includes a bar code symbol on the surface. A scanning component is also disposed in the light path. The scanning component may either sweep the beam spot across the symbol and trace a scan line across and past the symbol, or scan the field of view of the scanner or do both. A scanner also includes a sensor or photodetector. The photo-detector has a field of view which extends across and slightly past the symbol and functions to detect light reflected from the symbol. The analog electrical signal from the photodetector is first typically converted into a pulse width modulated digital signal, with the widths corresponding to the physical widths of the bars and spaces. Such a signal is then decoded according to the specific symbology into a binary representation of the data encoded in the symbol, and to the alphanumeric characters so represented.
The scanning component typically includes a moving mirror, such as a rotating polygon or a planar mirror which is repetitively and reciprocally driven in alternate circumferential directions about a drive shaft on which the mirror is mounted. However, the use of mechanical driven mirrors adds to the weight and size of the scanner, and also presents various reliability issues. Such drawbacks have led to consideration of techniques for generating and moving a scanning beam in a single integrated component.
Various approaches for generating a scanning beam by implementing arrays of lasers on a substrate are known in the prior art.
U.S. Pat. No. 4,445,125 describes a linear array of injection diode lasers formed on a common substrate to provide modulated scanning beams for a photosensitive medium. A scanning device, preferably a multifaceted mirror polygon driven at a constant speed, is placed in the optical path between the array and the photosensitive medium, as is a focusing lens. To provide additive exposure intensity the plane of the emitting surface of the array is oriented relative to the scanning device so that all of the beams emitted by the array are caused to illuminate the same scan line of the photosensitive medium whereby each beam scans the same data spots on the same line of the photosensitive medium.
U.S. Pat. No. 4,462,658 describes an optical scanner with a thin waveguide medium on a substrate includes means to couple a wide collimated beam of radiation into one end of the medium. A periodic array of substantially parallel, spaced electrodes are associated with one major surface of the medium. At least a portion of their electrode lengths extend in a direction substantially parallel with the direction of radiation propagating through the medium. Supply means is provided to apply voltage in a pattern to the electrodes which varies from one electrode to the next adjacent electrode to a predetermined value over several of the electrodes and the same pattern of voltages or a similar pattern of different voltages is applied over several of the next adjacent electrodes up to the predetermined value. In this manner, the pattern is completed across the electrode array to produce an electro-optical effect in which a corresponding approximation of a desired phase retardation along a phase front of the propagating radiation in the medium. Further means are employed to change the magnitude of the applied voltages across the electrode array to vary the approximation of the phase retardation to cause the radiation beam to scan in a direction of radiation propagation in the medium.
Still another approach for deflecting a beam on a substrate also based on the electro-optical effect use devices to direct a laser beam in one or more waveguides on a substrate. Optical waveguides are typically fabricated from a pyroelectric material such as lithium niobate or lithium tantalate or from semiconductor materials such as gallium arsenide or indium phosphide. Wavepaths or waveguides are generally fabricated in the substance by depositing a dopant such as titanium on the surface of the substrate in the pattern desired for the wavepaths. The substrate is then heated to diffuse the dopant into the substrate. This procedure forms wavepaths or waveguides, i.e., a section in the pyroelectric material that guides light, usually about 3 to 10 mu m wide. To permit logic operations, signal processing, or switching between wavepaths in the pyroelectric material, an electric field is imposed across the region of the crystal where a change in beam direction is desired. Such a field is generated by electrodes deposited on the substrate for this purpose. The field produces local changes in the optical polarizability of the crystal, thus locally changing the refractive index and, in turn, altering the path of light through the crystal.
Reference should also be made to publications describing a proposed integrated light source and scan element implemented on a single substrate and demultiplexes via intensity modulator array which can be used for scanning. Namely, J. Katz, "Phase Control and Beam Steering of Semiconductor Laser Arrays", TDA Progress Report 42-68, Jan.-Feb. 1982, and D. L. Robinson et al, Monolithically Integrated Array of GaAlAs Electroabsorption Modulators, Electronic Letters, Aug. 16th 1984, Vol. 20 No. 17 pp. 678-680.
Prior to the present invention there has not been an integrated light source and scanning element implemented on a single substrate.